Fabrication of semiconductor devices, including integrated circuits, may include one or more steps of etching a silicon-containing material or an aluminum-containing material, or forming a layer of material, on a semiconductor wafer using a plasma in a plasma processing tool. The process of etching or forming a layer on the semiconductor device may generate by-products which deposit inside a plasma chamber of the plasma processing tool performing the silicon etch process. The by-products may deposit on an optical window used, for example, for endpoint detection of the plasma process step. Buildup of by-products on the window may undesirably limit accuracy of the optical data obtained through the window, and/or may undesirably necessitate frequent cleaning of the window, reducing availability of the plasma processing tool.